1. Field of the Invention
This invention relates to a plain bearing, and more particularly to a plain bearing having a bearing alloy layer of which the inner surface is in a textured uneven surface and coated with an overlay layer.
2. Description of the Related Art
There is known a plain bearing of the type in which a bearing alloy layer is bonded to a back metal and an overlay layer made from a soft material such as a Pb-Sn alloy is provided on the inner surface of the bearing alloy layer so as to enhance the conformability and the embeddability for a foreign substance. There is also known a plain bearing of the type in which an intermediate layer made of Ni or the like is provided between the bearing alloy layer and the overlay layer so as to prevent components contained in the overlay layer from diffusing into the bearing alloy layer and improve adhesiveness of the overlay layer.
In those types of bearing, when the overlay layer wears to the extent that the hard intermediate layer extends widely, a mating shaft would directly slide on the hard intermediate layer and thus the seizure would be liable to occur abruptly. Therefore, there is also known a plain bearing of the type in which a plurality of recess grooves 64 are formed in the circumferential direction on the inner surface of the bearing alloy layer 61 by boring, and an intermediate layer 62 and an overlay layer 63 are further provided on the recess grooves 64, as shown in FIGS. 9 and 10, so that even when the overlay layer 63 wears, the intermediate layer 62 and/or the bearing alloy layer 61 does not extend widely but intermingles with the soft overlay layer 63 in the recess grooves 64 so as to maintain the anti-seizure property.
However, since the recess grooves 64 formed by boring extend in parallel with each other in the circumferential direction, when a foreign substance X such as a chip or a deterioration product of lubricant is introduced between the shaft and the plain bearing during the operation, the foreign substance is frictionally moved in the circumferential direction while leaving a long scar (or damage) on the surface of the overlay layer. As a result, the anti-seizure property of the bearing is reduced, and the damage may cause the spread of a fatigue crack. Therefore, it has been impossible to provide a plain bearing excellent both in the anti-seizure property and the fatigue resistance.
Accordingly, it is an object of the invention to provide a plain bearing excellent both in the anti-seizure property and the fatigue resistance.
According to a first aspect of the invention, there is provided a plain bearing of the type in which a recess groove formed on the inner surface of a bearing alloy layer has a bent portion so that when a foreign substance introduced between a mating shaft and the plain bearing is moved in the circumferential direction in accordance with the rotation of the shaft, the foreign substance runs against a side edge of the recess groove and moves along the side edge, and thereafter leaves the side edge again.
According to this aspect of the invention, when a foreign substance enters between the shaft and the plain bearing, it is moved in the circumferential direction while being embedded in the soft overlay layer by the pressing force of the shaft. After that, the foreign substance runs against a side edge of the recess groove and moves along the side edge while being pressed against the side edge. The pressing force promotes the embedding of the foreign substance into the overlay layer. Moreover, since the foreign substance which is failed to be adequately embedded into the overlay layer leaves the side edge at the bent portion and moves in the circumferential direction until it runs against the next side edge, the foreign substance does not bite on a side edge of the recess groove.
According to a second aspect of the invention, the recess groove is formed into a ring configuration corresponding to the inner surface of the bearing alloy layer. According to a third aspect of the invention, the recess groove is formed into a spiral configuration with respect to the circumferential direction on the inner surface of the bearing alloy layer.
The bearing alloy may be made of a Cu alloy or an Al alloy, for representative examples. The overlay layer may be made of one selected from the group of Pb, a Pb alloy, Sn, a Sn alloy, and a known sliding resin such as PTFE and PFA, for example.
Moreover, the bearing alloy layer may be directly covered with the overlay layer. Alternatively, the intermediate layer such as Ni or Ag may be provided between the bearing alloy layer and the overlay layer so as to enhance the adhesiveness and prevent components contained in the overlay layer from diffusing into the bearing alloy layer, as claimed in claim 2. The intermediate layer may be made of one selected from the group of Ni, Ag, a Ni alloy, Cu, a Cu alloy, Co, a Co alloy, Sn, a Sn alloy, an Ag alloy, Zn and a Zn alloy, for example.
The overlay layer may be made of a lead-tin alloy, for a representative example. However, the overlay layer may be made from other soft material such as a resin and a tin base alloy.
In the first aspect of the invention, a recess groove is formed in a bent shape so that when a foreign substance introduced between sliding surfaces of a shaft and a plain bearing is moved in the circumferential direction in accordance with the rotation of the shaft, it runs against a side edge of the recess groove and moves along the side edge, and thereafter leaves the side edge again. Further, the inner surface of the bearing alloy layer is made into a textured uneven condition owing to the recess groove formed thereon in the circumferential direction, and the overlay layer is provided on the inner surface of the bearing alloy layer to fill the recess groove, whereby there is provided a plain bearing excellent in the anti-seizure property and the embeddability for a foreign substance.